Digital implementation of continuous conduction mode-discontinuous conduction mode (CCM-DCM) power factor correction (PFC) control is typically based on average current control. In average current control, a reference inductor current is obtained by multiplying the output of the voltage mode controller with a rectified sinusoidal waveform obtained from the AC input voltage. The AC input voltage is needed to yield accurate current reference information for current regulation. Burst/standby mode control for average current mode CCM PFC is typically implemented with AC input voltage measurements, which requires the controller to have a at least one pin for measuring the AC input voltage during burst mode. In burst mode, the reference inductor current can be derived from the output of the voltage mode controller and the AC input voltage. Current mode control ensures that the average inductor current tracks the reference inductor current during the burst-on period. However, AC input voltage measurement may not be possible in burst mode. For example, there may be a resource conflict between AC detection and AC input voltage measurement features during burst mode. Pin count is a factor in controller cost. Some digital controllers minimize the number of pins to reduce cost. For these types of digital controllers, the controller may have a single pin for both the AC input voltage measurement feature and an AC detection feature. AC detection is used to detect if the AC input is disconnected, and to provide a low impedance path to quickly discharge an external capacitor when the AC input is disconnected. AC input voltage measurements are typically done via a high impedance path to reduce power loss. During burst mode, the AC detection feature is typically preferred over the AC input voltage measurement feature because of IEC safety requirement 62368-1. According to this standard, the voltage across the external capacitor must be lower than 60V after 2 seconds from AC disconnect. Hence, AC input voltage measurements may not be available for many types of power supply controllers during burst mode.
Thus, there is a need for an average current mode CCM PFC burst mode control strategy without AC input voltage measurements.